Sunnycat, its a statistical thing.
As around 80-90% of children are vaccinated against WC, it make sense that if it doesn't provide 100% protection, then 'more' children will get WC.
So, imagine there are 2 million children in Australia and 90% are vaccinated. That means 200,000 children are not vaccinated, but 1.8 million children are. If the vaccine is only 80% effective, then only 1.44 million children are protected, and 360,000 are not.
What you really want to compare is the rate of infection between vaccinated and non-vaccinated kids, because otherwise the 'rate' is skewed.
For vaccination to be ineffective, the rate of the disease (and the severity) needs to be the same or higher amongst vaccinated children when compared to non-vaccinated children.
In fact, for Australia:
So if immunisation programs have been successful, why is whooping cough still a problem?
Prevents severe illness and death
The short answer, according to immunisation expert Professor Peter McIntyre, is because the pertussis vaccine is good at reducing the risk of severe disease and death, but is not necessarily going to prevent infection altogether.
"It's not like measles vaccine where if you have the vaccine you just won't get measles infection," says McIntyre, director of the National Centre for Immunisation Research and Surveillance of Vaccine-Preventable Diseases at the University of Sydney.
"The pertussis vaccine is decreasing the amount of infection to some extent, but mostly what it's doing is decreasing how sick you get."
This means children who might otherwise have got extremely sick and ended up in intensive care on oxygen or even died, now get a milder infection or sometimes show no symptoms at all.
Also if you've had the vaccine you're less likely to transmit the disease to those around you.
However, it does mean that a significant proportion of infections will occur in vaccinated individuals.
"You'd expect that because if 95 per cent of kids are immunised and if you find that 95 per cent of the cases are also immunised, then that means that the vaccine's not doing anything," McIntyre says.
But that's not the case. Only about 70 per cent of reported cases of whooping cough occur in people who have had the pertussis vaccine.
"That's telling you that the vaccine is working and if you do the numbers, that equates to about an 80 per cent effectiveness of the vaccine."
is a good explanation about the rates.
So, the bottom line is that more non-vaccinated people get WC, as a percentage
, than vaccinated people. Vaccination is playing safe on the percentages.